The present invention relates to nebulizers for inhalation therapy, and more particularly concerns a nebulizer having an improved arrangement for heating both the container liquid and the aerosol produced by the nebulizer.
Nebulizers are commonly used for inhalation therapy to provide moist warm oxygen enriched breathing mixture to the patient. In many types of nebulizer a stream of oxygen is passed through a restrictive nozzle to increase its velocity and provide a venturi effect that sucks liquid from a container connected with a mixing chamber. The high speed stream of oxygen is mixed with ambient pressurized air and entrains water that is drawn up from the container by the low pressure of the venturi effect of the oxygen stream of high velocity.
The aerosol breathing mixture reaching the patient must have a temperature not less than ambient room temperature and moreover should have a significant content of water vapor. Various factors tend to lower the aerosol temperature including the relatively long path of aerosol flow through the tubing from the nebulizer to the patient and, in particular, the operation of the air water and oxygen mixing chamber, which often involves a decreased pressure due to at least the venturi action of the high speed jet. In the mixing chamber, expansion of the compressed oxygen will lower its pressure and thus effectively decrease the temperature of the resulting aerosol.
Many attempts have been made to heat either the aerosol or the container liquid but these have not been successful. Nebulizer heaters presently available are considered to be unsatisfactory. It is difficult to heat the aerosol directly, because the mixture, which is basically a gas, has low heat transmissivity, and thus efficiency of prior aerosol heaters has been low. Attempts to heat the aerosol by heating the water in the container before it is mixed with the air oxygen mixture also have been unsatisfactory in that it is difficult to transfer sufficient amounts of heat to the aerosol by means of heating the water. Moreover, having raised the temperature of the resulting aerosol by heating the water, the aerosol becomes more susceptible to "rain out", which means that water vapor in the aerosol tends to condense into larger droplets and to fall from the aerosol into the connecting tubing. The problem of water collecting in the connecting tubing between the nebulizer and the patient is significant, not only because of the fact that the aerosol reaching the patient has less moisture, but because water collecting in the tubing could block the tubing and prevent flow of any inhalation mixture to the patient.
Accordingly it is an object of the present invention to provide an aerosol heater that avoids or minimizes above mentioned problems.